1. Field of the Invention
The present invention relates to a color toner for the development of an electrostatic charge image in image formation methods such as electronic photography and static recording; a color toner which can be used in an image forming method of a toner jet system; and an image forming method.
2. Related Background Art
Usually, in the case of a system in which transfer material is loaded on a transfer drum, a full color image can be formed as follows. A photosensitive member on a photosensitive drum is evenly electrified by using a primary electrifier, and an image is exposed with laser rays modulated with, for example, a yellow image signal of a manuscript to form a static charge image on the photosensitive drum. The static charge image is developed with a yellow developing apparatus having yellow toner to form a yellow toner image. Subsequently, the yellow toner image developed on the photosensitive drum is transferred to a carried transfer material by a transfer electrifier.
On the other hand, the photosensitive drum, in which said static charged image has been developed, is diselectrified by an electrifier for diselectrification, cleaned by a cleaning means, and electrified again by the primary electrifier, a cyan image, for example, is formed and the cyan toner image is transferred to the transfer material to which said yellow toner image has been transferred by the same means, finally, magenta color and black color, for example, are serially processed to transfer toner image with four colors to the transfer material. A full color image is formed by fixing the transfer material having said toner image with the four colors by action of heat and a pressure using, a fixing roller.
It is required that when heated, the toner used for the image forming method of said colors shows good melting property and mixing property of colors. A toner having low softening point, low melting viscosity, and a high sharp melt property is preferably used.
This means that the use of a toner having a high sharp melt property widens the range of color reproducibility of copied product allows to yield a colored copy showing high fidelity to the original manuscript image.
However, such color toner with a high sharp melt property has the tendency that the offset development, in which a part of toner power is moved to the surface layer of the fixing roller in fixing process, is easily occurs, and on the other hand, the tendency that the transfer material easily curls after fixation by strong heat shrinkage after fixation.
Particularly in the fixing apparatus in the color image forming apparatus has the tendency that offset and curling easily occur because a plurality of toner layers, namely, yellow, cyan, magenta, and black, are formed on the transfer material.
In recent years, a variety of copying is required. For example, copying on both sides is gradually increasing for copying to both surfaces of the transfer material with a purpose of reducing consumption of paper, based on recent ecological movement. Therefore, the problems of the curling of transfer material and offset occurring in the image formation on the reverse side should be solved.
To solve these problems, a means has conventionally adopted using a parting compound, e.g., dimethyl silicone oil, evenly applied to the roller in fixing process to reduce offset in the fixing process. However, there are many remained points to be improved.
On the other hand, a method has been published for forced prevention of curling by using a tool like a curl remover after the first fixing to reduce curling of transfer material after fixing. However, a roller mark appears on the image and the structure of the main body become complex, because this method requires to apply the roller to the surface of an image immediately after fixing.
If curling of the transfer material occurs after fixing of a toner image to one side of the transfer material, the transfer material cannot be smoothly carried through a roller for repeated feeding of paper for fixing on both sides and a passage for carrying the transfer material.
In addition, in transfer of a color toner to the reverse side of the transfer material, a problem easily occurs to stain the surface of transfer drum by silicone oil adhered to the surface of the transfer material, of which the first fixing has been completed, in the formation of image on the reverse side. More amount of the adhered silicone oil to the transfer material does not easily allow the transfer material to round evenly around the transfer drum, and this problem causes increased frequencies of transfer and also a change of performance of the surface of sheet of the transfer drum to lower sometimes the transfer performance of toner.
U.S. Pat. No. 5,437,949 proposes a color toner having a particular particle distribution to improve coloring performance of the color toner and U.S. Pat. No. 5,529,865 proposes a method for image formation to carry out smooth fixing of both sides by adjusting the particle distribution of the color toner. However, color toner and a method for image formation desired are those excellent in resistant performance to copying of multiple sheets and capable of smoother fixing of full color images for both sides, respectively.
U.S. Pat. No. 5,652,075 proposes a color toner assigned for particle distribution of pigment particles contained in the color toner particles, U.S. Pat. No. 5,607,806 proposes a toner in which alumina powder of a low crystallinity supplied from outside, EP Patent Publication No. 800117A1 proposes toner improved for fixing performance, color mixing, and resistance to offset. However, A color toner and a method for image formation desired are those excellent in resistant performance to copying of multiple sheets and capable of smoother fixing of full color images for both sides, respectively.